1. Field of the Invention
The present invention relates to an angular velocity detection element and an angular velocity measuring device suitable for detecting an angular velocity of a rotation member, for example.
2. Description of the Related Art
An angular velocity detection element for use in an angular velocity measuring device generally detects a Coriolis force in response to an angular velocity applied to the angular velocity detection element. For example, when an external angular velocity is applied around the Z axis of an angular velocity detection element under the condition that a movable body of the angular velocity detection element vibrates constantly in the X axis, a Coriolis force acts on the movable body in the Y axis perpendicular to the X axis. The displacement of the movable body caused by the Coriolis force is detected in a change in piezoelectric resistance or capacitance, and the magnitude of angular velocity is thus detected.
FIGS. 16 and 17 shows one example of a conventional angular velocity detection element disclosed in Japanese Laid-open Patent Publication No. 6-123632.
Shown here are the angular velocity detecting device 1 of the conventional art and a square-shaped substrate 2 that is the main body of the angular velocity detecting device 1, and the substrate 2 is manufactured of high-resistance silicon, for example.
Also shown are a pair of vibrating support bodies 3, 3 which are arranged on the substrate 2 to interpose a square movable body 7 between the left side and right side of the substrate 2, a pair of detecting support bodies 4, 4 which are arranged on the substrate 2 to interpose the moveable body 7 between the front side and rear side of the substrate 2 (between the top side and bottom side on the page of both FIGS. 16 and 17).
A pair of support-side vibrating electrodes 5,5 are arranged on the left-hand side and right-hand side as shown, and are integrally formed with and arranged to face the support bodies 3, 3. Four electrode plates 5A, 5A, . . . are projected from the respective support-side vibrating electrodes 5, 5 in a comb-shaped fashion.
Support-side detecting electrodes 6,6 are arranged on the upper side and lower side as shown, and are integrally formed with and arranged to face the support bodies 4, 4. Four electrode plates 6A, 6A, . . . are projected from the respective support-side detecting electrodes 6, 6.
The movable body 7 is manufactured of low-resistance polysilicon or single-crystal silicon, doped with P, B, Sb or the like, and the movable body 7 is supported on the substrate 2 with a spacing allowed between the movable body 7 and the top surface of the substrate 2 by its four support portions 8 on the substrate 2 near its four corners, and four support beams 9, each bent in an L-shaped configuration and having a portion extending in parallel in the X axis and a portion extending in parallel in the Y axis.
Since the movable body 7 is supported by its L-shaped support beams 9, the movable body 7 is displaced in the direction of the X axis when the portion of each beam 9 in parallel with the Y axis is deflected and the movable body 7 is displaced in the direction of the Y axis when the portion of each beam 9 in parallel with the X axis is deflected, and the movable body 7 is thus displaceable in both directions of the X axis and the Y axis. Furthermore, on its left-hand and right-hand sides as shown, the movable body 7 is integrally formed with movable-side vibrating electrodes 10, 10 to be described later, which are interdigitally engaged with the support-side vibrating electrodes 5, and on its upper side and lower side as shown, the movable body 7 is integrally formed with movable-side detecting electrodes 11, 11, which are interdigitally engaged with the support-side detecting electrodes 6.
Each of the movable-side vibrating electrodes 10, 10 is constructed of four electrode plates 10A arranged in a comb-like fashion on the left-hand and right-hand sides of the movable body 7 in the direction of the X axis, wherein the four electrode plates 10A are interdigitally engaged with the respective electrode plates 5A of each of the support-side vibrating electrodes 5 with a gap therebetween.
Each of the movable-side vibrating electrodes 11, 11 is constructed of four electrode plates 11A arranged in a comb-like fashion on the upper and lower sides of the movable body 7 in the direction of the Y axis, wherein the four electrode plates 11A are interdigitally engaged with the respective electrode plates 6A of each of the support-side detecting electrodes 6 with a gap therebetween.
Designated 12, 12 are vibration generators, and each of the vibration generators 12 is constituted by the support-side vibrating electrode 5 and the movable-side vibrating electrode 10, and equal gaps are formed between each electrode plate 5A of the support-side vibrating electrode 5 and each electrode plate 10A of the movable-side vibrating electrode 10.
When two driving signals which have a frequency f and opposite phases with each other and are generated by an oscillator (not shown) are applied to the vibration generators 12 on the left and right sides, respectively, an electrostatic attractive force takes place between the electrode plates 5A, 10A in the vibration generators 12 alternately on the left-hand side and on the right-hand side, and thus each of the vibration generators 12 repeats closing and parting actions. The movable body 7 thus vibrates in the direction of an arrow a in alignment with the X axis.
Designated 13, 13 are angular velocity detectors, and each angular velocity detector 13 is constituted by the support-side detecting electrode 6 and movable-side detecting electrode 11, and equal gaps are formed between each electrode plate 6A of the support-side detecting electrode 6 and each electrode plate 11A of the movable-side detecting electrode 11. The support-side detecting electrodes 6, 11 are constructed as a plane-parallel capacitor, and each angular velocity detector 13 detects, as a change in capacitance, a change in effective area between the electrode plates 6A and 11A.
When the driving signals of opposite phase of frequency f are applied to the vibration generators 12 in the angular velocity detection element 1 thus constructed, an electrostatic attractive force takes place between the electrode plates 5A and 10A alternately between the left-hand vibration generator 12 and the right-hand vibration generator 12, and the movable body 7 vibrates in the direction of the arrow a in alignment with the X axis due to repeated electrode closing and parting actions.
When an angular velocity P acts on the angular velocity detection element 1 about the Z axis with the movable body 7 vibrating, a Coriolis force (inertia) is generated in the direction of the Y axis, and the movable body 7 is displaced in the direction of the Y axis under a Coriolis force F as expressed in equation 2 below.
When the vibration generator 12 displaces the movable body 7 in the X axis, a displacement x and a velocity V are as expressed in equation 1. EQU x=A sin .omega..sub.1 t [Equation 1] EQU V=A .omega..sub.1 cos .omega..sub.1 t
where A: Amplitude of the movable body 7
.omega..sub.1 : Angular frequency of driving mode PA1 t: Time PA1 .OMEGA.: Angular velocity
When an angular velocity .OMEGA. is applied about the Z axis with the movable body 7 displaced by a displacement x in the direction of the X axis at a velocity of V, a Coriolis force F takes place in the direction of Y axis as expressed in equation 2. EQU F=2m.OMEGA.V [Equation 2]
where m: Mass of the movable body 7
The movable body 7, under the Coriolis force F expressed in equation 2, vibrates in the direction of the Y axis, and the angular velocity detector 13 detects the displacement of the movable body 7 as a change in capacitance between the movable-side detecting electrodes 11 and the support-side detecting electrodes 6, and thus detects the angular velocity .OMEGA. about the Z axis.
Since each vibration generator 12 is constituted by the support-side vibrating electrode 5 having the electrode plates 5A and the movable-side vibrating electrode 10 having the electrode plates l0A, large facing effective areas are assured between the electrodes 5 and 10. When the driving signals are fed to the vibration generators 12, the electrostatic attractive force taking place between the electrode plates 5A and the corresponding electrode plates 10A becomes large enough to vibrate greatly the movable body 7 in the direction of the arrow a.
In addition, since each angular velocity detector 13 is also constituted by the support-side detecting electrode 6 having the electrode plates 6A and the movable-side detecting electrode 11 having the electrode plates 11A, large facing effective areas are assured between the detecting electrodes 6 and 11. Each angular velocity detector 13 detects the displacement of the movable body 7 in the direction of the Y axis in the form of a change in capacitance arising from a change in the effective areas between the electrode plates 6A and the corresponding electrode plates 11A.
As is clear from equations 1 and 2, the Coriolis force F is proportional to the velocity V of the movable body 7 in the angular velocity detection element 1, and the velocity V of the movable body 7 is proportional to the amplitude of the movable body 7. It is easy to understand that the detection sensitivity of the angular velocity detection element 1 is enhanced as the amplitude of vibration of the movable body 7 gets larger. For this reason, in the angular velocity detection element 1 of the conventional art, the frequency f of the driving signal output by the oscillator circuit is set to coincide with the natural oscillation frequency of the angular velocity detection element 1 so that the movable body 7 vibrates at resonance.
However, since the angular velocity detection element 1 of the conventional art is so complicated as described above, the natural oscillation frequencies of the angular velocity detection elements 1 as manufactured do not have equal values because of manufacturing errors or the like. For this reason, when the angular velocity detection element 1 is connected to the oscillator circuit, an adjusting step is required on an individual basis so that the frequency of the driving signal output by the oscillator circuit is adjusted to match the natural oscillation frequency of the angular velocity detection element 1.
Furthermore, in the angular velocity detection element of the conventional art, even if the frequency of the output from the oscillation means matches the natural oscillation frequency of the angular velocity detection element 1, the detection sensitivity of an angular velocity measuring device is substantially degraded when the natural oscillation frequency of the angular velocity detection element 1 changes because of aging or the like.
For the aforementioned reasons, there arises a demand for an angular velocity detection element and an angular velocity measuring device, which can realize constant vibration of a movable body at a resonance frequency.